The present invention relates to a fused plug and particularly to such a plug of the add-on type which permits other plugs to be plugged into such plug and thus "added on".
Light string sets of the type utilized for decorative purposes, as for holiday lighting and for Christmas trees, typically utilizing miniaturized incandescent lamps, are manufactured with relatively small guage insulated wire as befits the small operating current in the wire. Fusing is providing for the light string sets for protecting against short circuits and to provide the sets with adequate intrinsic safety (which safety will be given approval by safety rating authorities or organizations as are well-known) and to comply with various national or state or regional electrical codes.
Therefore, it has been known heretofore to utilize various conventional fuses in various ways as a part of the light string set. Among such prior art is included the concept of placing fuse lamps within the end sockets of a series circuit string. This protects the lamps between the ends of the string. Such an arrangement is disclosed in U.S. Pat. No. 4,223,248 of the present inventor, entitled "Fused Light String Set". Another arrangement provides a fused plug of the add-on type wherein the plug body which includes a pair of fuse lamps is disclosed in U.S. Pat. No. 4,350,407 of the present inventor. U.S. Pat. No. 4,030,059, also of the present inventor, discloses a fuse of the type utilizable for light string sets.
When incorporated into a plug body, fuses may either be replaceable or not. If not replaceable, the melting of the fuseable element of the fuse within the plug body means that the entire light string set must be replaced. Such construction is objectionable to persons who have economy in mind or who desire the capability of correcting the difficulty and changing the fuse.
Because of the intense competition in the marketplace, it is very important to provide a design for a fused plug which is very economical to produce. If means is incorporated for permitting the fuses within the plug body to be replaced, a complexity is added to the construction which increases the costs. The provision of moveable parts also may compromise the strength of construction. For example, Magherini U.S. Pat. No. 3,976,967 teaches a plug including a body having a fuse carrier which is pivotably moveable to a position in which cartridge fuse elements can be replaced, but the construction is relatively cumbersome and expensive to manufacture.
Such U.S. Pat. No. 3,976,967 constituted a substantial improvement over the objectionable bulky fused plug construction of Cardone U.S. Pat. No. 2,808,485 which includes a removeable cup-shaped member withdrawn to render access to relatively large, conventional cartridge fuses. The latter patent in turn represented an improvement over the fused plug constructions of McIntosh U.S. Pat. No. 2,030,016 and Gerlat U.S. Pat. No. 2,668,885 which include plug body components which could be disassembled. Holoka U.S. Pat. No. 3,833,875 may also be noted as showing a fused plug construction having a plastic case with a removeable cover. But such construction is objectionable from the viewpoints of economy and strength.
Referring to FIGS. 1(a) and 1(b), a fused add-on plug 1 of another prior art construction is shown. Said plug 1 has a plug body having an upper shell or body portion 2(a) and a lower shell or body portion 2(b) which are joined together by rivets 3, the two halves or shells defining slots or openings 4, 4' for receiving the prongs of a plug to be added on. Extending forwardly from the opposite end of the joined plug body portions are plug blades 5, 5'. The lower plug body portion 2(b) defines recesses 6, 6' for receiving a pair of miniature cartridge fuses 7, 7'. The upper half 2(a) is provided with a U-shaped recess in which is received a removable, slidable door or cover 9 which may be withdrawn for providing access to the fuses 7, 7' for inspection or replacement. However, this prior art fuse plug construction has the disadvantage of being formed of a separate rather than integral body components which, or course, must be joined together in a separate manufacturing step with rivets 3. Accordingly, the economy of manufacture is not as great as desired, and the plug further suffers from the disadvantage that it is not as strong as a plug body of integral, unitary construction.
The prior art construction of FIGS. 1(a) and 1(b) additionally exhibit a number of inherent disadvantages. For example, the plug blades 5, 5' are receivable in slots 10, 10' but nothing specifically holds them in place except the mutual fit as between the upper and lower shells or halves 2(a), 2(b). Consequently, if after use, plug 1 should develop a crack as between the upper and lower shells 2(a), 2(b), either of the plug blades 5, 5' might be permitted to shift in different directions, thus causing poor electrical contact. Another problem is that the cartridge fuses 7, 7' are pressed into place and into electrical contact by force of the sliding door or cover 9, the underside of which has a spring effect upon the fuses. However, if an add-on plug has been received numberous times by openings 4, 4', the leverage applied between the shells 2(a) 2(b) may cause a gap to open between them, reducing the spring effect on the slide or door 9. Thus, fuses 7, 7' could come loose and again result in poor electrical contact. Also, the use of rivets 3 to secure the two body shells 2(a) 2(b) is labor intensive and accordingly not economical. In addition, if the rivets are not properly riveted, a crack may result in either of the shells 2(a) 2(b), not only weakening the structure but possibly also causing poor electrical contact. A further difficulty is that the electrode or plug blade 5, 5' have a fixed, unique orientation. Hence, they cannot be interchanged. I.e., the blade on the right cannot be used on the left or vice versa. This requires production of separate elements and requires additional time and effort during assembly. Finally, the sliding door 9, if opened and closed a number of times for fuses, may ultimately become loose, and in fact, may even fall off, thereby exposing the fuses unsafely as well as causing poor electrical contact or failure.
It is an object of the present invention to provide an improved fused plug which is particularly useful with light string sets.
It is another object of the present invention to provide such an improved fused plug having construction of relative simplicity with relatively few parts which are easily produced as by injection molding to provide extreme economizing of manufacture.
An object of the present invention is also to provide such a fused plug of add-on type which is not weakened or distorted by the repeated insertion and removal of the plug blades of a plug being added on.
It is a further object of the present invention to provide such a fused plug which is of compact configuration, being neither bulky nor cumbersome in use, and having small dimensions so as not requiring the use of thick sections of material, the material of construction being thereby reduced in volume and the plug being made lightweight, but such that the plug body is of relatively great strength and provides extreme resistance to damage.
It is also an object of the present invention to provide such a fused plug which includes miniaturized fuses which are easily replaced by the common consumer without resort to special tools or without requiring expertise or finesse.
Another object of the present invention is the provision of such a fused plug which has a unitary outer shell with intrinsically high strength and resistance to damage.
A further object of the present invention is the provision of a fused plug of the type described which requires that the plug described be removed from a wall socket before fuses within the plug are accessible for replacement, thereby providing greater safety for the user.
A further object of the invention is the provision of such a fused plug which includes plug blades which are anchored to a fuse site body which is in turn anchored within the body shell so that the parts are tightly and reliably held in mutual securement so as not to be easily subjected to shaking or loosening, and so as always to provide excellent electrical contact.
Among other objects of the invention may be noted the provision of such a fused plug having high inherent safety without reliability being compromised; which is not prone to failure due to vibration, weather exposure or temperature changes or other damages; and which in general provides a high degree of safety for the consumer.
Other objects will be in part apparent and others described in the following description.